The History of Philosophy is the exposition of philosophical opinions
and of systems and schools of philosophy. It includes the study of the
lives of philosophers, the inquiry into the mutual connection of
schools and systems of thought, and the attempt to trace the course of
philosophical progress or retrogression. The nature and scope of
philosophy furnish reasons for the study of its history. Philosophy
does not confine its investigation to one or to several departments of
knowledge; it is concerned with the ultimate principles and laws of all
things. Every science has for its aim to find the causes of phenomena;
philosophy seeks to discover ultimate causes, thus carrying to a higher
plane the unifying process begun in the lower sciences. The vastness of
the field of inquiry, the difficulty of synthesizing the results of
scientific investigation, and the constantly increasing complexity of
these results necessitated the gradual development of philosophy. To
each generation and to each individual the problems of philosophy
present themselves anew, and the influences, personal, racial,
climatic, social, and religious, which bear on the generation or on the
individual must be studied in order that the meaning and value of each
doctrine and system be understood and appreciated. Such influences are
more than a matter of mere erudition; they have their place in the
praenotanda to the solution of every important question
in philosophy; for, as Coleridge says, "the very fact that any
doctrine has been believed by thoughtful men is part of the problem to
be solved, is one of the phenomena to be accounted for." Moreover,
philosophical doctrines, while they are to be regarded primarily as
contributions to truth, are also to be studied as vital forces which
have determined to a large extent the literary, artistic, political,
and industrial life of the world. To-day, more than ever, it is clearly
understood that without a knowledge of these forces it is impossible to
comprehend the inner movements of thought which alone explain the outer
actions of men and nations.

The dangers to be avoided in the study of the history of philosophy are
Eclecticism, which teaches that all systems are equally true,
and Scepticism, which teaches that all systems are equally
false. A careful study of the course of philosophical speculation will
result in the conviction that, while no single school can lay claim to
the entire truth, certain schools of thought have adopted that
world-concept which can be most consistently applied to every
department of knowledge. False systems of philosophy may stumble on
many important truths, but a right concept of the ultimate meaning of
reality and a correct notion of philosophic method are the essentials
for which we must look in every system; these constitute a legitimate
standard of valuation by which the student of the history of philosophy
may judge each successive contribution to philosophical science.

The method to be followed in this study is the empirical, or
a posteriori, method, which is employed in all historical
research. The speculative, or a priori, method consists in
laying down a principle, such as the Hegelian principle that the
succession of schools and systems corresponds to the succession of
logical categories, and deducing from such a principle the actual
succession of schools and systems. But, apart from the danger of
misstating facts for the sake of methodic symmetry, such a
procedure must be judged to be philosophically unsound; for systems
of philosophy, like facts of general history, are contingent events.
There are, indeed, laws of historical development; but such laws are to
be established subsequently, not anteriorly, to the study of the facts
of history.

The historian of philosophy, therefore, has for his task: (1) To set
forth the lives and doctrines of philosophers and systems and schools
of philosophy in their historical relation. This, the recitative
or narrative portion of the historian's task, includes the
critical examination of sources. (2) To trace the genetic connection
between systems, schools, and doctrines, and to estimate the value of
each successive contribution to philosophy. This, the
philosophical portion of the historian's task, is by far the
most important of his duties: Potius de rebus ipsis judicare
debemus, quam pro magno de hominibus quid quisque senserit
scire.(1)

The sources of the history of philosophy are: (1) Primary
sources, namely, the works, complete or fragmentary, of
philosophers. It is part of the historian's task to establish, whenever
necessary, the authenticity and integrity of these works.
(2) Secondary sources, that is, the narration or testimony of
other persons concerning the lives, opinions, and doctrines of
philosophers. In dealing with secondary sources the rules of
historical criticism must be applied, in order to determine the
reliability of witnesses.

The division of the history of philosophy will always be more or
less arbitrary in matters of detail. This is owing to the continuity of
historical development: the stream of human thought flows continuously
from one generation to another; like all human institutions, systems
and schools of philosophy never break entirely with the past; they
arise and succeed one another without abrupt transition and merge into
one another so imperceptibly that it is rarely possible to decide where
one ends and
another begins. The more general divisions, however, are determined by
great historical events and by obvious national and geographical
distinctions. Thus, the coming of Christ divides the History of
Philosophy into two parts, each of which may be subdivided as follows:

PART I -- ANCIENT OR PRE-CHRISTIAN PHILOSOPHY

SECTION A -- ORIENTAL OR PRE-HELLENIC PHILOSOPHY

SECTION B -- GREEK AND GRECO-ROMAN PHILOSOPHY

SECTION C -- GRECO-ORIENTAL PHILOSOPHY

PART II -- PHILOSOPHY OF THE CHRISTIAN ERA

SECTION A -- PATRISTIC PHILOSOPHY

SECTION B -- SCHOLASTIC PHILOSOPHY

SECTION C -- MODERN PHILOSOPHY

Footnotes

St. Augustine, De Civitate Dei, XIX, 3.

General Bibliography. -- The following works treat of the
History of Philosophy as a whole: Erdmann, History of
Philosophy, trans. by Hough (3 vols., London, 1890); Ueberweg,
History of Philosophy, trans. by Morris (2 vols., New York,
1872); Weber, History of Philosophy, trans. by Thilly (New York,
1896); Windelband, History of Philosophy, trans. by Tufts
(second edition, New York, 1901); Stöckl, Lehrbuch der
Geschichte der Philosophie (2 Bde., 3. Aufl., Mainz, 1888), trans.
in part from the second edition by Finlay (Dublin, 1887).